Transcript Diapositiva 1

Scalar Mesons Physics
with the KLOE detector
C.Bini
Universita’ “La Sapienza” and INFN Roma
For the KLOE collaboration
Outline
1. Status of the KLOE experiment
2. “Hadron Physics” at a f - factory
3. Scalar Mesons at a f - factory :
4. Results
4.1 p+p-g
4.2 p0p0g
4.3 hp0g
5. Summary and perspectives
1) Status of the KLOE experiment
These days: end of f –peak run  2 fb-1 collected in the last two years.
f
6 ×109
K+ - K-
3 ×109
KL - KS
2 ×109
h
6 ×107
f0, a0
6 ×105
h’
5 ×105
ANALYZED
Program now: energy scan around the f + off-peak run s = 1 GeV:
KLOE end by spring 2006
2) “Hadron Physics” at a f - factory
Preview: analysis done and in progress (non Kaon physics)
f  hp0g
Study of a0(980)
f  p0 p0 g
Study of f0(980) + f0(600)
f  hg , h’g
h / h’ mixing
f  p + p -p 0
r+,-,0 line shapes + “direct term”
h ggg / h p+p-
Upper limit on C, P, CP violating decays
fe+e- / f m+m-
f leptonic widths: lepton universality
e+e- p+p- (rad. ret,)
Hadronic contribution to g-2
f  p + p -g
Study of f0(980) + f0(600)
h  p + p -p 0
Fit of Dalitz plot: ChPT test
h  p0 p0 p0
Fit of Dalitz plot: ChPT test
h  p0gg
ChPT test @ p6
h, K0 masses
3) Scalar Mesons at a f - factory
How a f-factory can contribute to the understanding of
the scalar mesons
Mass (MeV/c2)
f(1020)
1000
a0(980)
f0(980)
K*0(800)
“k”
500
f0(600)
“s”
0
I=0
I=1/2
I=1
Scalar Mesons Spectroscopy:
f0(980), f0(600) and a0(980)
are accessible (k not accessible)
through f  Sg;
Questions:
1. Is f0(600) needed to describe
the mass spectra ?
2. “couplings”of f0(980) and
a0(980) to f  |ss> and to KK,
pp and hp.
 4-quark vs. 2-quark states
How to detect these radiative decays
f f0(980)g
f a0(980)g
f f0(600)g
 p+p-g
 p0p0g
 K+K-g [ 2m(K)~m(f0)~m(f) ]  expected BR
 K0K0g
“
“
 hp0g
 K+K-g
expected BR
 K0K0g

“
 p+p-g
 p0p0g
~ 10-6
~ 10-8
~ 10-6
~ 10-8
General Comments:
 fits of mass spectra are needed to extract the signals:
this requires a parametrization for the signal shape;
 the unreducible background is not fully known: a
parametrization is required and some parameters have to be
determined from the data themselves;
 sizeable interferences between signal and
background;
How to extract the signal:
1. Electric Dipole Transitions:
 G(E1)  Eg3 × |Mif(Eg)|2
2. Distortions due to KK
thresholds (Flatte’-like).
Kaon-loop (by N.N.Achasov): for each scalar meson S: gSpp, gSKK, MS
No-Structure (by G.Isidori and L.Maiani): a modified BW + a polynomial
continuum: gfSg, gSpp, gSKK, MS + pol. cont. parameters
Scattering Amplitudes (by M.E.Boglione and M.R.Pennington)
A  (a1+b1m2+c1m4) T(pppp) + (a1+b1m2+c1m4) T(ppKK)
 pole residual gf
Definition of the relevant couplings (S=f0 or a0):
S to f
S to kaons
f0 to pp (I=0)
a0 to hp (I=1)
Coupling ratio
gfSg
gSKK=gSK+K-=gSK0K0
gf0pp=√3/2 gf0p+p-=√3 gf0p0p0
ga0hp
Rf0=(gf0KK/ gf0p+p-)2
Ra0=(ga0KK/ ga0hp)2
p+
g
Kaon-loop
p+
K+
f
f0,a0
K-
(GeV-1)
(GeV)
(GeV)
(GeV)
p-
No-structure
f
p-
f0,a0
g
The unreducible backgrounds
Unreducible backgrounds:
(p+p- ): huge backgrounds:
Initial state radiation (ISR)
Final state radiation (FSR)
f r±p± with r ±  p±g
(p0p0): large backgrounds:
e+e-  wp0 with w  p0g
f r0p0 with r 0  p0g
(hp0): small backgrounds:
e+e-  wp0 with w  hg
f r0p0 with r 0  hg
(p+p-) vs. (p0p0): search for the “same amplitude” with a completely
different background !
(hp0)
is the “cleanest” sample
4.1) The p+p-g analysis
I - Event selection:
(a) 2 tracks with qt>45o; missing momentum qpp>45o (Large Angle);
(b) Each track is pion-like (tracking, ToF and Shower shape):
(c) 1 photon matching the missing momentum
Particle identification: p vs. e and m
(Likelihood: Tof and Shower shape)
pions, muons
(“trackmass”)
pions
muons
electrons
II – The data sample
6.7 ×105 events / 350 pb-1 @ √s = Mf
2.2 ×104 events / 11 pb-1 “off-peak”
m(pp) spectra:
(blue) “Small angle” qpp<15o;
(red) “Large angle” qpp>45o;
“Large angle”:
clear f0(980) signal
f0(980) region
m(pp) (MeV)
photon
efficiency
m(pp) (MeV)
III - Fit to the m(pp) spectrum
(491 bins, 1.2 MeV wide, 420 to 1009 MeV)
F= ISR + FSR + rp + scalar ± interference
KL fit
NS fit
KL and NS fits:
Good description in both cases
of signal and background (KS);
 “negative” interference;
f0(600) doesn’t help.
Parameter uncertainties are dominated by the systematic errors:
Comments:
Mass value OK [ PDG 980 ± 10 MeV ]
R > 1 in both fits (in agreement with published
values p0p0g)
KL couplings >> NS couplings: effect of polynomial
continuum
NS suggests “large” coupling to the f (see following)
Scattering Amplitude Fit
gf = 6.6 ×10-4  BR(ff0(980)g) × BR(f0(980)p+p-) ~ 3 × 10-5
[ similar conclusion from BP analysis of p0p0g data (KLOE + SND)]
Summarizing:
The peak at ~980 MeV is well interpreted in both KL and
NS approaches as due to the decay f  f0(980)g with a
negative interference with FSR.
The couplings suggest the f0(980) to be strongly coupled
to kaons and to the f.
No space for f0(600).
Scattering Amplitude gives a marginal agreement.
IV - The Forward-Backward asymmetry:
A = (N(q+>90o) – N(q+<90o)) / sum
p+p- system:
A(ISR)
C-odd
A(FSR) & A(scalar)
C-even
Cross-section: |A(tot)|2 = |A(ISR)|2 + |A(FSR)|2 + |A(scalar)|2
+ 2Re[A(ISR) A(FSR)] + 2Re[A(ISR) A(scalar)]
+ 2Re[A(FSR) A(scalar)]
Pion polar angle distributions
(Red) = p+
(Blue) = p-
Effect of the scalar amplitude on the charge asymmetry:
Plot of A in slices of m(pp);
Comparison with simulation with and without the scalar amplitude.
FB asymmetry vs. m(pp):
 Clear signal ~ 980 MeV
 Interesting comparison with simulation:
Data
Simulation FSR+ISR
Simulation FSR+ISR+
scalar(KL)
The simulation provides a “qualitative” description of:
f0(980) region behaviour (the signal is reproduced);
Low mass behaviour (low mass tail of the signal.
Remarkable result: not a fit but an absolute prediction
V – Cross section dependence on √s:
Absolute prediction based on KL fit parameters
Data: on-peak
Data: off-peak
KL absolute prediction
Based on fit parameters
Concluding remark: p+p-g is a powerful tool to test scalar
production: mass spectrum, FB asym. and s dependence
KLOE has now collected 2 fb-1 at f  factor 6 more.
Is now starting a finer energy scan around the f
4.2) The p0p0g analysis
I - event selection:
5 photons with qg>21o ; no tracks;
Kinematic fit  energy-momentum conservation;
Kinematic fit  p0 masses: choice of the pairing.
 4 ×105 events / 450 pb-1
2002 analysis scheme:
1. Reject wp0 events  interference is
neglected;
2. 1-dim analysis: fit with KL
The spectrum is dominated
by w  p0g
KLOE PLB537 (2002) 21
New analysis scheme:
1. Removed the m(w) cut : wp0 are now in the sample
2. Bi-dimensional analysis [ Dalitz-plot m(p0p0) – m(p0g) ]
3. New treatment of systematics [ pairing problem...]
4. Improved VDM parametrization of wp0
II – Fit of the Dalitz plot (still preliminary results)
KL and NS fits in progress
Residuals vs. DP
position
Data- fit comparison (on projections)
Comments: 1. VDM part still not perfect (see residuals);
2. Scalar part ok BUT f0(600) is still needed
in KL fit [p(c2) ~ 10-4  30% !];
3. f0(980) parameters agree with p+p-g analysis
again R > 1 (gfKK > gfp+p-).
4.3) The hp0g analysis
I – The data samples: out of 400 pb-1 :
Statistics of PLB536 (2002) 209 × 20
(h  gg) Improved reducible
background subtraction:
2.2 ×104 events [ ½ are signal]
Red = signal
Other colors= bck
(h  p+p-p0) almost “background
free”  4100 events [ bck < 3%]
Full pts.
= “20 pb-1” data
Empty pts. = “400 pb-1” data
M(hp) (MeV)
II – The combined fit
Simultaneous fit of hgg and hp+p-p0 channels: ratio of BR is fixed
Pts. = data, hist = fit (including smearing)
KL fit
NS fit
The spectra are dominated by the a0 production:
both models are able to reproduce them
Preliminary results of the fits (KL and NS):
KL fit
gfa0g
(GeV-1)
NS fit
1.9
ga0K+K- (GeV)
2.3
1.9
Ga0hp (GeV)
2.6
2.2
Comments:
gfa0g ~ in agreement with f0 value
Ra0= 0.78 (KL) and 0.74 (NS) < 1
5) Summary and Perspectives
The KLOE scalar analysis is not yet completed. However:
1. f0(600): required in the p0p0 channel not in
the p+p- one: no clear answer by now.
2. Couplings:
both NS and KL fits indicate
Rf0 =(gf0K+K-/ gf0p+p-)2 = 2 ÷ 4
Ra0 = (ga0K+K-/ ga0hp-)2 = 0.7 ÷ 0.8
from NS analysis: large couplings to the f
gff0g = 1.2 ÷ 2.0
gfa0g ~ 1.9 (unc. evaluation in progress)
in any case >> gfpg gfhg gfh’g = (0.1  0.7).
KLOE perspectives on scalar mesons
1. Conclude analysis on 2001-2002 data sample
for f0(980) (neutral final states) and a0(980).
2. With 2000 pb-1 @ f peak:
improvement expected for f0 → p+pcombined fit p+p- AND p0p0
search for f0, a0  KK
3. With new forthcoming energy scan data
improved study of the √s-dependence of
the cross-section;
Off-peak: “test run” of gg  p0p0